Ring seal for a turbine engine

ABSTRACT

Aspects of the invention are directed to a ceramic matrix composite ring seal segment. The ring seal segment according to aspects of the invention includes a relatively simple body that is circumferentially curved. At least a portion of the hot gas path surface of the ring seal segment can be coated with a thermal insulating. material. In one embodiment, each ring seal segment can be operatively connected to a stationary support structure, such as by way of isolation rings. The ring seal segments and/or the isolation rings can be configured so as to restrain the ring seal segments in the axial, radial and/or circumferential directions. The ring seal segments can be attached to the isolation rings so that the support points act opposite the operating pressure loads. Thus, the ring seal segments carry these loads in compression, a strong direction of the CMC fibers.

FIELD OF THE INVENTION

Aspects of the invention relate in general to turbine engines and, moreparticularly, to ring seals in the turbine section of a turbine engine.

BACKGROUND OF THE INVENTION

FIG. 1 shows an example of one known turbine engine 10 having acompressor section 12, a combustor section 14 and a turbine section 16.In the turbine section 16 of a turbine engine, there are alternatingrows of stationary airfoils 18 (commonly referred to as vanes) androtating airfoils 20 (commonly referred to as blades). Each row ofblades 20 is formed by a plurality of rotating airfoils 20 attached to adisc 22 provided on a rotor 24. The blades 20 can extend radiallyoutward from the discs 22 and terminate in a region known as the bladetip 26. Each row of vanes 18 is formed by attaching a plurality of vanes18 to a vane carrier 28. The vanes 18 can extend radially inward fromthe inner peripheral surface 30 of the vane carrier 28. The vane carrier28 is attached to an outer casing 32, which encloses the turbine section16 of the engine 10.

Between the rows of vanes 18, a ring seal 34 can be attached to theinner peripheral surface 30 of the vane carrier 28. The ring seal 34 isa stationary component that acts as a hot gas path guide between therows of vanes 18 at the locations of the rotating blades 20. The ringseal 34 is commonly formed by a plurality of metal ring segments. Thering segments can be attached either directly to the vane carrier 28 orindirectly such as by attaching to metal isolation rings (not shown)that attach to the vane carrier 28. Each ring seal 34 can substantiallysurround a row of blades 20 such that the tips 26 of the rotating blades20 are in close proximity to the ring seal 34.

During engine operation, high temperature, high velocity gases flowthrough the rows of vanes 18 and blades 20 in the turbine section 16.The ring seals 34 are exposed to these gases as well. Some metal ringseals 34 must be cooled in order to withstand the high temperature. Inmany engine designs, demands to improve engine performance have been metin part by increasing engine firing temperatures. Consequently, the ringseals 34 require greater cooling to keep the temperature of the ringseals 34 within the critical metal temperature limit. In the past, thering seals 34 have been coated with thermal barrier coatings to minimizethe amount of cooling required. However, even with a thermal barriercoating, the ring seal 34 must still be actively cooled to prevent thering seal 34 from overheating and burning up. Such active coolingsystems are usually complicated and costly. Further, the use of greateramounts of air to cool the ring seals 34 detracts from the use of airfor other purposes in the engine.

As an alternative, the ring seals 34 could be made of ceramic matrixcomposites (CMC), which have higher temperature capabilities than metalalloys. By utilizing such materials, cooling air can be reduced, whichhas a direct impact on engine performance, emissions control andoperating economics. However, there are a number of natural limitationsand manufacturing constraints associated with CMC materials. Forinstance, CMC materials (oxide and non-oxide based) can have anisotropicstrength properties. The interlaminar tensile strength (the “throughthickness” tensile strength) can be substantially less than the in-planestrength. Many prior ring seal designs include small radius corners andtightly-curved sections. Such areas are difficult to form in a CMCcomponent using known fabrication techniques. Further, anisotropicshrinkage during processing can lead to result in de-lamination defectsin such areas, which can further reduce the interlaminar tensilestrength of the CMC material.

Thus, there is a need for a ring seal construction that can minimize theeffects of the anisotropic characteristics of CMC materials.

SUMMARY OF THE INVENTION

Aspects of the invention are directed to a turbine engine ring sealsystem. The system includes a ring seal segment that has a firstcircumferential end and a second circumferential end. The ring sealsegment is circumferentially curved as it extends between the first andsecond circumferential ends. The ring seal segment also has an axialforward end, an axial aft end, a radially outer surface and a radiallyinner surface. The radially inner surface is radially inwardly concave.

The ring seal segment is made of ceramic matrix composite, such as, forexample, an oxide-oxide ceramic matrix composite. Thus, the ring sealsegment can include a ceramic matrix in which there are a plurality offibers. At least a substantial majority of the fibers can be orientedparallel to an axis about which the ring seal segment iscircumferentially curved.

A thermal insulating material can be attached to the radially innersurface of the ring seal segment. The thermal insulating material can bea friable graded insulation. The thermal insulating material can berecessed from the axial forward end of the ring seal segment so that aforward shelf is formed. Likewise, the thermal insulating material canbe recessed from the axial aft end of the ring seal segment so that anaft shelf is formed.

The system further includes a stationary support structure. The ringseal segment is operatively connected to the stationary supportstructure at the axial forward end and at the axial aft end of the ringseal segment. In one embodiment, a forward isolation ring and an aftisolation ring can be attached to the stationary support structure. Insuch case, the forward shelf can engage the forward isolation ring, andthe aft shelf can engage the aft isolation ring. As a result, the ringseal segment can be indirectly connected to the stationary supportstructure by the isolation rings.

Each of the forward and aft isolation rings can include a radiallyextending body and a ledge that extends substantially axially. The ledgecan include a radially inner surface and a radially outer surface. Theforward shelf can engage the ledge of the forward isolation ring, andthe aft shelf can engage the ledge of the aft isolation ring. When suchengagement occurs, the thermal insulating material can be substantiallyflush with the radially inner surface of each of the ledges.

In one embodiment, the ring seal segment can operatively engage thestationary support structure so that the ring seal segment is restrainedin the radially outward direction. To that end, each of the isolationrings can have an elongated channel. A portion of the ring seal segmentincluding the axial forward end can be received within the channel inthe forward isolation ring. Similarly, a portion of the ring sealsegment including the axial aft end can be received in the channel inthe aft isolation ring. Thus, the ring seal segment can be restrained inat least the radially outward direction.

Alternatively or in addition, the ring seal segment can operativelyengage the stationary support structure such that the ring seal segmentis substantially circumferentially restrained. To that end, each of theisolation rings can provide an axially extending protrusion, and each ofthe axial forward and aft ends of the ring seal segment can include anotch. The protrusion of the forward isolation ring can be received inthe notch in the forward end of the ring seal segment. The protrusion ofthe aft isolation ring can be received in the notch in the aft ring sealsegment. As a result, the ring seal segment can be restrained in thecircumferential direction.

Another turbine engine ring seal system according to aspects of theinvention includes a stationary support structure, a forward isolationring and an aft isolation ring opposite the forward isolation ring. Theforward and aft isolation rings are attached to the stationary supportstructure and extend substantially radially inward from it. Each of theisolation rings can have a radially inner surface.

The system further includes a ring seal segment that has a firstcircumferential end and a second circumferential end. The ring sealsegment is circumferentially curved as it extends between the first andsecond circumferential ends. The ring seal segment can becircumferentially curved relative to an axis. The ring seal segmentfurther has an axial forward end, an axially aft end, a radially outersurface and a radially inner surface. The radially inner surface isradially inwardly concave.

The ring seal segment is made of ceramic matrix composite, such as anoxide-oxide ceramic matrix composite. Thus, the ring seal segmentincludes a ceramic matrix with a plurality of fibers. At a minimum, asubstantial majority of the fibers can be oriented parallel to the axis.

At least a portion of the radially inner surface of the ring sealsegment is coated with a thermal insulating material, which can be, forexample, a friable graded insulation. The thermal insulating materialcan be recessed from the axial forward end of the ring seal segment sothat a forward shelf is formed. Further, the thermal insulating materialcan be recessed from the axial aft end of the ring seal segment so thatan aft shelf is formed.

The axial forward end of the ring seal segment is operatively attachedto the forward isolation ring. The axial aft end of the ring sealsegment is operatively attached to the aft isolation ring. In oneembodiment, the forward shelf of the ring seal segment can operativelyengage the forward isolation ring, and the aft shelf of the ring sealsegment can operatively engage the aft isolation ring. The thermalinsulating material can be substantially flush with the radially innersurface of each of the isolation rings.

Each of the isolation rings can have an elongated channel therein. Aportion of the ring seal segment that includes the axial forward end canbe received within the channel in the forward isolation ring. Similarly,a portion of the ring seal segment that includes the axial aft end canbe received in the channel in the aft isolation ring. Thus, the ringseal segment can be restrained in at least the radially outwarddirection.

In one embodiment, each of the isolation rings can also provide anaxially extending protrusion, which can be located within the channel.Each of the axial forward and aft ends of the ring seal segment caninclude a notch. The protrusion of the forward isolation ring can bereceived in the notch in the forward end of the ring seal segment. Theprotrusion of the aft isolation ring can be received in the notch in theaft ring seal segment. As a result, the ring seal segment can berestrained in the circumferential direction.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross-sectional view of the turbine section of a knownturbine engine.

FIG. 2 is an isometric view of a ring seal segment according to aspectsof the invention.

FIG. 3 is an exploded isometric view of a ring seal segment attachmentsystem according to aspects of the invention.

FIG. 4 is an isometric bottom view of a ring seal segment attachmentsystem according to aspects of the invention.

DETAILED DESCRIPTION OF EMBODIMENTS OF THE INVENTION

Embodiments of the invention are directed to a ceramic matrix composite(CMC) ring seal construction and attachment system that can minimize themanufacturing limitations and natural anisotropic effects of CMCmaterials. Aspects of the invention will be explained in connection withone possible ring seal segment for a turbine engine, but the detaileddescription is intended only as exemplary. An embodiment of theinvention is shown in FIGS. 2-4, but the present invention is notlimited to the illustrated structure or application.

FIG. 2 shows a ring seal body according to aspects of the invention. Thering seal body can be, for example, a ring seal segment 50. The ringseal segment 50 can have an axial forward end 52 and an axial aft end54. The terms “forward” and “aft” are intended to mean relative to thedirection of the gas flow 56 through the turbine section when the ringseal segment 50 is installed in its operational position. The ring sealsegment 50 can also have a radially inner surface 58 and a radiallyouter surface 60. The ring seal segment 50 can have a firstcircumferential end 62 and a second circumferential end 64. The ringseal segment 50 can be curved circumferentially as it extends from thefirst circumferential end 62 to the second circumferential end 64. Theradially inner surface 58 can be radially inwardly concave. The terms“axial,” “radial” and “circumferential” and variations thereof areintended to mean relative to the turbine axis 66 when the ring sealsegment 50 is installed in its operational position.

The ring seal segment 50 can be made of ceramic matrix composite (CMC).For example, the ring seal segment 50 can be made of an oxide-oxide CMC,such as AN-720, which is available from COI Ceramics, Inc., San Diego,Calif. In one embodiment, the ring seal segment 50 can be made of ahybrid oxide CMC material, an example of which is disclosed in U.S. Pat.No. 6,733,907, which is incorporated herein by reference. The thicknessof the ring seal segment 50 can be substantially uniform throughout. Thering seal segment 50 can be formed by any suitable fabricationtechnique, such as winding, weaving, and lay-up. The manufacture of aring seal segment 50 according to aspects of the invention isfacilitated by the relatively simple arc-like shape. It will beappreciated that the absence of areas with a small radius of curvaturecan avoid the prior difficulties that could arise in such areas due tothe anisotropic characteristics of CMC materials.

The CMC material of the ring seal segment 50 includes a ceramic matrix68 and a plurality of fibers 70 within the matrix 68. The fibers 70 ofthe CMC can be oriented to provide the desired strength properties. Forinstance, the fibers 70 can be oriented to provide anisotropic,orthotropic, or in-plane isotropic properties. In one embodiment, asubstantial majority of the fibers 70 can extend substantially parallelto the flow path 56 of the turbine. For instance, at least some of thefibers 70 can extend from the axial forward end 52 toward the axiallyaft end 54. Alternatively or in addition, at least some of the fibers 70can extend from the first circumferential end 62 toward the secondcircumferential end 64. In one embodiment, the fibers 70 can be arrangedat substantially 90 degrees relative to each other, such as a 0-90degree orientation or a ±45 degree orientation. Again, these are merelyexamples as the fibers 70 of the CMC can be arranged as needed.

Because the ring seal segment 50 is exposed to the hot combustion gases56, at least a portion of the radially inner surface 58 of the ring sealsegment 50 can be coated with a thermal insulating material 72. Thethermal insulating material 72 can be, for example, a friable gradedinsulation (FGI). Various examples of FGI are disclosed in U.S. Pat.Nos. 6,676,783; 6,670,046; 6,641,907; 6,287,511; 6,235,370; and6,013,592, which are incorporated herein by reference. A layer ofadhesive or other bond-enhancing material (not shown) can be usedbetween the CMC ring seal segment 50 and the thermal insulating material72 to facilitate attachment.

In one embodiment, the thermal insulating material 72 can cover aportion of the radially inner surface 58. As shown in FIG. 2, thethermal insulating material 72 can be recessed from at least the axialforward end 52 and the axially aft end 54 of the ring seal segment 50.As a result, a forward shelf 74 can be formed by the uncoated portion ofthe radially inner surface 58 proximate the axial forward end 52, and anaft shelf 76 can be formed by the uncoated portion of the radially innersurface 58 proximate the axial aft end 54. Similarly, the thermalinsulating material 72 can be recessed from the first and secondcircumferential ends 62, 64. In such case, additional shelves 78 can beformed by the uncoated portions of the radially inner surface 58proximate each of the circumferential ends 62, 64.

A plurality of the ring seal segments 50 configured in accordance withaspects of the invention can be installed so that each of thecircumferential end 62, 64 of a ring seal segment 50 is substantiallyadjacent to one of the circumferential ends 62, 64 of a neighboring ringseal segment. The plurality of ring seal segments 50 can collectivelyform an annular ring seal.

The ring seal segments 50 can be operatively connected to a stationarysupport structure 80 in the turbine section. The stationary supportstructure 80 can be, for example, a turbine casing or a vane carrier.Preferably, most, if not all, of the features directed to facilitatingthe operative connection of the ring seal segments 50 are provided inthe stationary support structure 80 or other associated structures so asto retain the relatively simple geometry of the ring seal segments 50.

In one embodiment, the operative connection between each ring sealsegment 50 and the stationary support structure 80 can be indirect. Forinstance, each ring seal segment 50 can be operatively connected to thestationary support structure 80 by way of a forward isolation ring 82and an aft isolation ring 84. The isolation rings 82, 84 can be attachedto the stationary support structure 80 in any of a number of known ways.For instance, a portion of each isolation ring 82, 84 can be configuredas a hook to be received in a respective slot (not shown) provided inthe stationary support structure 80. The isolation rings 82, 84 canextend radially inwardly from the stationary support structure 80. Eachof the isolation rings 82, 84 can form a substantially 360 degree ring.

The isolation rings 82, 84 can have various configurations. In oneembodiment, each of the isolation rings 82, 84 can be a single piece orcan be made of a plurality of pieces. The forward and aft isolationrings 82, 84 may or may not be substantially identical to each other.The isolation rings 82, 84 can have any suitable configuration. In oneembodiment, the isolation rings 82, 84 can be generally L-shaped havinga body 86 and an axially extending ledge 88. The ledge 88 can have aradially inner surface 90 and a radially outer surface 92.

The ring seal segments 50 can be installed so that the forward and aftshelves 74, 76 of each ring seal segment engage a respective ledge 88 ofthe forward and aft isolation rings 82, 84. For instance, the forwardshelf 74 can engage the radially outer surface 92 of the ledge 88 of theforward isolation ring 82. Likewise, the aft shelf 88 can engage theradially outer surface 88 of the ledge 88 of the aft isolation ring 84.In such case, it is preferred if the thermal insulating material 72 issubstantially flush with the radially inner surface 90 of each ledge 88,as shown in FIG. 4. As a result of such an arrangement, neither theisolation rings 82, 84 nor the thermal insulating material 72 protrudeinto the hot gas path 56. Thus, flow interruptions in the hot gas path56 and consequent aerodynamic losses are minimized. It will beappreciated that the engagement between the shelves 74, 76 and ledges 88can restrain the ring seal segments 50 in the radially inward direction.Further, the forward and aft isolation rings 82, 84 can restrain axialmovement of the ring seal segments 50.

The ring seal segments 50 can be restrained in other directions as well.The ring seal segments 50 and/or the isolation rings 82, 84 can beadapted to provide the desired restraint. For instance, the forwardisolation ring 82 can provide a channel 94 for receiving a portion ofthe ring seal segment 50 including the axial forward end 52. Likewise,the aft isolation ring 84 can provide a channel 94 for receiving aportion of the ring seal segment 50 including the axial aft end 54. Insuch case, the ring seal segments 50 can be restrained in at least theradially outward direction by the channels 94.

Alternatively or in addition, the isolation rings 82, 84 and/or the ringseal segments 50 can be adapted to provide circumferential restraint. Inone embodiment, the axial forward end 52 of the ring seal segment 50 canprovide at least one notch 96. Likewise, the axial aft end 54 of thering seal segment 50 can include at least one notch 96. The notches 96can be centrally located on each end 52, 54 of the ring seal segment 50.The notches 96 can be formed in the ring seal segment 50 by any suitableprocess. Each of the isolation rings 82, 84 can provide one or moreprotrusions 98 to be received in a respective notch 96 in the forwardand aft ends 52, 54 of the ring seal segments 50. The protrusions 98 canbe located within the channels 94. It will be appreciated that theengagement between the protrusions 98 and the notches 96 can restraincircumferential movement of the ring seal segments 50. Significantly, inany of the above schemes, the ring seal segment 50 can be retained bythe isolation rings 82, 84 without the use of additional fasteners orother mounting hardware.

The isolation rings 82, 84 can be made of metal. Because of the hightemperature environment of the turbine, the isolation rings 82, 84 mustbe cooled. The isolation rings 82, 84 can be cooled in any of a numberof ways. In one embodiment, the isolation rings 82, 84 can include oneor more internal-cooling passages (not shown). A coolant, such ascompressed air, can be supplied to the passages. The coolant can exitthe isolation rings 82, 84 through outlet passages 100 and enter the hotgas path 56 of the turbine.

Like the isolation rings 82, 84, the ring seal segment 50 according toaspects of the invention can be cooled during engine operation. Acoolant, such as air, can be supplied to the radially outer surface 60of the ring seal segment 50. However, there is a potential for suchcoolant, which is at a relatively high pressure, to leak through theinterfaces between adjacent circumferential ends 62, 64 of neighboringring seal segments 50. Another leakage path is between the engagingportions of the isolation rings 82, 84 and the ring seal segments 50.Seals (not shown) can be operatively positioned to minimize theseleakage paths. The ring seal segment 50 and/or isolation rings 82, 84can be adapted as necessary to facilitate sealing.

During engine operation, the ring seal segment 50 can be subjected to avariety of loads. The ring seal segment 50 according to aspects of theinvention is well suited to withstand the expected operational loads.The ring seal segments 50 and their associated attachment system areconfigured so that the support points act opposite the operatingpressure loads. Thus, the loads are carried by the ring seal segments 50in compression, which is one of the strongest strength directions of theCMC fibers. Further, the ring seal segment attachment system allowsthermal growth and contraction of the ring seal segment without undueconstraint, thereby minimizing thermally induced stresses.

The foregoing description is provided in the context of one possiblering seal segment for use in a turbine engine. Thus, it will of coursebe understood that the invention is not limited to the specific detailsdescribed herein, which are given by way of example only, and thatvarious modifications and alterations are possible within the scope ofthe invention as defined in the following claims.

1. A turbine engine ring seal system comprising: a ceramic matrixcomposite ring seal segment having a first circumferential end and asecond circumferential end, the ring seal segment beingcircumferentially curved as it extends between the first and secondcircumferential ends, the ring seal segment further having an axialforward end, an axial aft end, a radially outer surface and a radiallyinner surface, the radially inner surface being radially inwardlyconcave; and a stationary support structure, wherein the ring sealsegment is operatively connected to the stationary support structure atthe axial forward end and at the axial aft end.
 2. The system of claim 1wherein the ceramic matrix composite is an oxide-oxide ceramic matrixcomposite.
 3. The system of claim 1 further including a thermalinsulating material attached to the radially inner surface of the ringseal segment.
 4. The system of claim 3 wherein the thermal insulatingmaterial is a friable graded insulation.
 5. The system of claim 3further including a forward isolation ring and an aft isolation ringattached to the stationary support structure, wherein the thermalinsulating material is recessed from the axial forward end of the ringseal segment so that a forward shelf is formed, and wherein the thermalinsulating material is recessed from the axial aft end of the ring sealsegment so that an aft shelf is formed, and wherein the forward shelfengages the forward isolation ring and the aft shelf engages the aftisolation ring, whereby the ring seal segment is indirectly connected tothe stationary support structure by the isolation rings.
 6. The systemof claim 5 wherein each of the forward and aft isolation rings includesa radially extending body and a ledge that extends substantiallyaxially, wherein the ledge includes a radially inner surface and aradially outer surface, wherein the forward shelf engages the ledge ofthe forward isolation ring and the aft shelf engages the ledge of theaft isolation ring, and wherein the thermal insulating material issubstantially flush with the radially inner surface of each of theledges.
 7. The system of claim 1 wherein the ring seal segmentoperatively engages the stationary support structure so as to berestrained in the radially outward direction.
 8. The system of claim 7further including a forward isolation ring and an aft isolation ringattached to the stationary support structure, wherein each of theisolation rings has an elongated channel therein, wherein a portion ofthe ring seal segment including the axial forward end is received withinthe channel in the forward isolation ring, and wherein a portion of thering seal segment including the axial aft end is received in the channelin the aft isolation ring, whereby the ring seal segment is restrainedin at least the radially outward direction.
 9. The system of claim 1wherein the ring seal segment operatively engages the stationary supportstructure so as to be substantially circumferentially restrained. 10.The system of claim 9 further including a forward isolation ring and anaft isolation ring attached to the stationary support structure, each ofthe isolation rings providing an axially extending protrusion, whereineach of the axial forward and aft ends of the ring seal segment includea notch, wherein the protrusion of the forward isolation ring isreceived in the notch in the forward end of the ring seal segment, andwherein the protrusion of the aft isolation ring is received in thenotch in the aft end of the ring seal segment, whereby the ring sealsegment is restrained in the circumferential direction.
 11. The systemof claim 1 wherein the ring seal segment is circumferentially curvedrelative to an axis, wherein the ceramic matrix composite of the ringseal segment includes a ceramic matrix with a plurality of fiberstherein, wherein at least a substantial majority of the fibers areoriented parallel to the axis.
 12. A turbine engine ring seal systemcomprising: a stationary support structure; a forward isolation ring; anaft isolation ring opposite the forward isolation ring, the forward andaft isolation rings attached to the stationary support structure andextending substantially radially inward therefrom; and a ceramic matrixcomposite ring seal segment having a first circumferential end and asecond circumferential end, the ring seal segment beingcircumferentially curved as it extends between the first and secondcircumferential ends, the ring seal segment further having an axialforward end, an axially aft end, a radially outer surface and a radiallyinner surface, the radially inner surface being radially inwardlyconcave, wherein at least a portion of the radially inner surface of thering seal segment is coated with a thermal insulating material, whereinthe axial forward end of the ring seal segment is operatively attachedto the forward isolation ring and the axial aft end of the ring sealsegment is operatively attached to the aft isolation ring.
 13. Thesystem of claim 12 wherein the ceramic matrix composite is anoxide-oxide ceramic matrix composite.
 14. The system of claim 12 whereinthe thermal insulating material is a friable graded insulation.
 15. Thesystem of claim 12 wherein the thermal insulating material is recessedfrom the axial forward end of the ring seal segment so that a forwardshelf is formed, and wherein the thermal insulating material is recessedfrom the axial aft end of the ring seal segment so that an aft shelf isformed, and wherein the forward shelf operatively engages the forwardisolation ring and the aft shelf operatively engages the aft isolationring.
 16. The system of claim 12 wherein each of the isolation rings hasa radially inner surface, wherein the thermal insulating material issubstantially flush with the radially inner surface of each of theisolation rings.
 17. The system of claim 12 wherein each of theisolation rings has an elongated channel therein, wherein a portion ofthe ring seal segment including the axial forward end is received withinthe channel in the forward isolation ring, and wherein a portion of thering seal segment including the axial aft end is received in the channelin the aft isolation ring, whereby the ring seal segment is restrainedin at least the radially outward direction.
 18. The system of claim 17wherein each of the isolation rings providing an axially extendingprotrusion, wherein each of the axial forward and aft ends of the ringseal segment includes a notch, wherein the protrusion of the forwardisolation ring is received in the notch in the forward end of the ringseal segment, and wherein the, protrusion of the aft isolation ring isreceived in the notch in the aft ring seal segment, whereby the ringseal segment is restrained in the circumferential direction.
 19. Thesystem of claim 18 wherein the protrusion is located within the channel.20. The system of claim 12 wherein the ring seal segment iscircumferentially curved relative to an axis, wherein the ceramic matrixcomposite of the ring seal segment includes a ceramic matrix with aplurality of fibers therein, wherein at least a substantial majority ofthe fibers are oriented parallel to the axis.